From: Michael Fellinger <m.fellinger@...>
Date: 2010-08-27T14:27:37+09:00
Subject: Re: Get Proc of current block?

On Fri, Aug 27, 2010 at 10:42 AM, Intransition <transfire@gmail.com> wrote:
> Is there any way to get a hold of the current block? I've been playing
> around with recursive enumerations and it occurs to me that the most
> flexible technique would simply be to reuse the currently running
> block.
>
> For example, where `this` would be the current block:
>
>  h = {:a=>1, :b=>{:c=>3}}
>
>  h.map{ |k,v| Hash===v ? [k.to_s, v.map(&this)] : [k.to_s,v.to_s] }
>
>  #=> {"a"=>"1", "b"=>{"c"=>"3"}}

That's called the Y-combinator, something i wish could be added to
core, but would be afraid of the many nay-sayers who are already
confused by the current number of ways of creating blocks :)

def y(*args, &block)
  y = lambda{|*args| block.(*args, &y) }
end

p y{|n, acc, &b|
  n < 2 ? acc : b.(n-1, n * acc)
}.(5, 1)



-- 
Michael Fellinger
CTO, The Rubyists, LLC